The invention relates to an apparatus and method for transformer testing and more particularly to an apparatus and method for impulse measurement testing of transformer terminals.
Impulse measurement is a common testing practice in the manufacture of electrical transformers. Impulse measurement simulates lightning strikes and other events that cause transients to appear in electrical circuitry. Impulse measurement testing is performed on transformers to monitor the effects of transients and to insure the insulation capabilities of the dielectric material in the transformer. Impulse measurement testing requires that each individual terminal of a transformer be xe2x80x98hitxe2x80x99 with impulses of varying degree to determine whether that particular terminal is in proper working order and ready for shipment to the consumer.
Impulse measurement testing is done by connecting one of the transformer terminals to an impulse generator and the remaining terminals to either a shunt to ground or directly to ground. Then, an impulse is sent through the terminal and proper measurements are taken to determine if the terminal met the test criteria. The impulse generator is then moved to another terminal and the previously tested terminal is connected to either a grounded shunt or ground with the remaining terminals. An impulse is then sent to the second terminal and measurements are again taken for that terminal. This process is repeated until all terminals are tested.
The terminals that are not being tested can be connected either directly to ground or through a resistive shunt to ground (grounded shunt). The nature of the tested terminal determines which terminals are connected to the grounded shunt or directly to ground. If the tested terminal is a high voltage terminal, then the remaining high voltage terminals are connected to ground through the resistive shunt and all of the low voltage terminals are grounded directly. If the tested terminal is a low voltage terminal, then the remaining low voltage terminals are connected to through the resistive shunt to ground and all the high voltage terminals are grounded directly.
Impulse measurement testing takes about 6-8 hours to complete. There are several reasons why impulse measurement testing is so time consuming. One reason is that testers are required to manually connect and reconnect equipment between terminals. On large transformers, due to the size, testers must walk up and down a flight of stairs or a ladder to connect and reconnect the terminals. The connecting and reconnecting process consumes about 80% of the testing time. Therefore, a decrease in the connecting/reconnecting time would significantly reduce the overall testing time.
Another reason is the device used to test the medium or large transformers is also large and can not be easily handled by one person, thus requiring multiple manhours at a time to complete.
For the foregoing reasons, there is a need for a device and/or process that reduces testing time by overcoming the aforementioned disadvantages. The present invention satisfies all these needs.
The present invention is directed to a switching assembly and related process that satisfies the need of reducing switching time during impulse measurement testing to decrease the overall cycle time of a transformer. Reduced switching time is achieved because the assembly can be assembled and disassembled by one person, it can be broken down into various units that are easily carried by one person, and all switching can be done from a central point.
According to the present invention, a switch assembly for performing impulse testing on each of a plurality of terminals of a transformer comprises a plurality of single pole, double throw switches and a switch controller for each switch. Each switch has a first position that connects a respective transformer terminal to one of a ground and a shunt and a second position that connects the terminal to an impulse generator. Preferably, the switch controllers are co-located to enable a user to change the position of any one of the switches from a central position.